1. Field of the Invention
The invention relates to the production of potentially reactive gas mixtures and to the determination of schemes for mixing such gases.
2. Description of the Related Art
In order to reduce potentially reactive gas mixtures completely safely, various mixing methods and/or apparatuses have been proposed at the present time, which methods take into account the capability of the static mixture; that is to say only the quality of the final mixture is considered.
This is the case, for example, with document U.S. Pat. No. 5,801,265 which relates to a method of injecting oxygen into a reactant, for which a control device ensures that an oxygen/reactants mixture has a final composition lying above a certain upper flammability limit.
Studies on gas mixtures in burners generally concern the reaction of the gases and in particular the combustion products which must satisfy a precise specification (particularly, low NOx formation and limitation in the maximum temperature).
At the present time, there is no method making it possible to determine a gas injection scheme which takes into account the change in the composition of the mixture while it is being produced.
The invention provides another approach so as to determine the possibilities of producing a potentially flammable gas mixture.
More specifically, the invention provides a study of the use of a mixture of reactive gases, taking into account the actual mixing phenomenon, i.e. the risks owing to the reactivity which may arise during the mixing phase.
The invention relates especially to a procedure for determining the risk of flammability of a mixture of at least two reactive gases A, B, in an inert gas or a base gas (a gas possibly containing the gases A, B and other species, which may or may not be reactive) or for determining the order of mixing of the reactive gases in the inert or base gas.
The term xe2x80x9cinert gasxe2x80x9d should particularly be understood to mean a gas that does not lead, under the mixing conditions, to chemical reactions with A or B or with itself.
Modes of mixture formation (or mixing modes) are defined, according to the order in which the reactive gases are successively mixed into the inert or base gas: according to a first mode, the gas A is firstly mixed into an inert or base gas, forming with the latter a first mixture into which the gas B is then mixed; according to a second mode, the gas B is firstly mixed into the inert or base gas, forming with the latter a first mixture into which the gas A is then mixed. If the mixture involves more than two gases in the inert or base gas, further modes of mixture formation may be defined.
Starting from the ternary diagram for the mixture in question (whether this is a mixture of two or more gases in the inert gas or base gas), it is possible to determine the change in the composition of the mixture when A is firstly injected into the inert gas, or the base gas, in order to form a first mixture and then B is injected into the first mixture in order to form the final mixture.
Examination of the ternary diagram provides direct information about the composition of the mixture with respect to its flammability region, something which is not the case if binary diagrams are used.
If the composition of the mixture changes within the ternary diagram without entering the flammability region, this mode of injection may be adopted since its flammability risk is zero.
It is also possible to compare, for one or both mixing modes, the transit time spent by the mixture, during its formation, passing through the flammability region of this diagram, or the mixing time (which is greater than the transit time), with the chemical induction time for this same mixture.
The mixing time is linked with the technology of the mixer. This is because it depends on the velocities of the flow generated by the mixer and on its ability to mix rapidly.
The subject of the invention is therefore a procedure for determining the risk of flammability of a mixture of at least two reactive gases A, B, in an inert or base gas, or the order of mixing of these reactive gases into the inert or base gas, characterized in that it comprises:
a step for determining whether the composition of the mixture, during its formation, passes through the flammability region in the ternary diagram of the A/B/base (or inert) gas mixture when this mixture is produced according to a first mode in which A is firstly mixed into the inert or base gas in order to form a first mixture and then B is mixed into the first mixture in order to form the final mixture.
This procedure may furthermore include:
a step of determining a first transit time through the flammability region of the said ternary diagram, this transit time depending on the mixture used during the phase of producing the mixture which forces the composition to pass through the flammability region;
a step of comparing this first transit time with the chemical induction time of the mixture; the latter time depends of the reactivity of the mixture.
According to a variant, it is the mixing time, characteristic of the mixer used during the phase of producing the mixture which forces the composition to pass through the flammability region, which is compared with the chemical induction time of the mixture.
If the composition of the mixture passes through the flammability region of the said ternary diagram, or else if the mixing time involved or the first transit time is greater than the chemical induction time of the mixture, the following steps may also be carried out:
a step for determining whether the composition of the mixture, during its formation, passes through the flammability region in the ternary diagram of the A/B/base (or inert) gas mixture, when the latter is produced according to a second mode in which B is firstly mixed into the inert or base gas in order to form a first mixture and then A is mixed into the first mixture in order to form the final mixture, and, optionally:
a step of comparing the mixing time of the mixer, used during the phase of producing the mixture which forces the composition to pass through the flammability region, with the chemical induction time of the mixture when B is firstly mixed into the inert or base gas in order to form a first mixture and then A is mixed into the first mixture in order to form the final mixture; or else
the determination of a second transit time within the flammability region of the said ternary diagram when B is firstly injected into the inert or base gas in order to form a first mixture and then A is injected into the first mixture in order to form the final mixture, and a step of comparing this second transit time with the chemical induction time of the mixture.
Preferably, it is the minimum chemical induction time which is compared with the mixing time. The induction time for the stoichiometric mixture is generally close to this minimum induction time and may be taken as an approximation of this minimum time.
The procedure according to the invention therefore takes the mixing phenomenon into account. It makes it possible, based on the flammability characteristics of the gas mixture composed of A, B and the inert or base gas, and on the characteristics of the mixers used, to evaluate the flammability risk while A is being mixed into B, the latter already being mixed with the inert or base gas, or while B is being mixed into A, the latter already being mixed with the inert or base gas, more than simply knowing whether or not the final A+B+inert or base gas mixture would be flammable.
The invention also makes it possible to evaluate the most judicious and safest solution in order to know which fluid to mix first and foremost and to know how to produce the mixture. This is especially the case when the invention is applied to injections of two reactive fluids into a predominantly inert stream, as in recycling processes.
The procedure according to the invention may apply to a mixture of several gases, the number of gases to be mixed being greater than three.
One procedure for mixing two reactive gases A, B into an inert or base gas therefore comprises:
determining the flammability risk of the mixture, while the mixture is being produced, or determining the order of injection of the reactive gases, using the procedure according to the invention and described above;
mixing the reactive gases A and B in the order for which the composition of the mixture does not pass through the flammability region while the composition is changing, or for which the mixing time(s) or the transit time through the flammability region of the ternary diagram is (are) less than the chemical induction time of the mixture.
According to the invention, the case in which at least three reactive or fuel gases are mixed with an inert or base gas may amount to the successive treatment of several cases of mixing two gases with an inert or base gas.
Implementation of the invention may be helped by consulting electronic databases.
The invention also relates to a procedure for producing a plant for mixing at least two reactive gases A, B into an inert or base gas, comprising the following steps:
the order of mixing these gases is determined using a procedure as described above;
a plant is produced so as to mix the gases in the order thus determined.
Thus, mixers may be placed in a line supplying the inert or base gas, so that the mixing of the gases takes place under very safe conditions.
The invention therefore makes it possible to produce, with a high degree of safety, a plant for mixing at least two reactive gases A, B into an inert or base gas.
The subject of the invention is also an apparatus for implementing the invention, characterized in that it comprises:
means for storing at least one database containing, for gas mixtures, data on the ternary diagrams of these mixtures, and the flammability regions in these diagrams for given temperature and pressure conditions;
means for selecting a gas mixture and pressure and temperature conditions to be used for this gas mixture;
means for displaying a ternary diagram and the flammability region of a mixture in this diagram.
According to another aspect, the subject of the invention is also an apparatus for establishing the flammability risk of mixtures, each mixture consisting of at least two reactive gases A, B in an inert or base gas, or for establishing the order of mixing of these reactive gases into the inert or base gas, characterized in that it includes means for computing, or means especially programmed for computing, as a function of temperature and pressure conditions:
the ternary diagram of a mixture and the flammability region in this diagram;
a chemical induction time of these mixtures. The latter parameter depends on the temperature, pressure and concentration.
Finally, the subject of the invention is a terminal for establishing the flammability risk of a mixture of at least two reactive gases A, B in an inert or base gas, or the order of mixing these reactive gases into the inert or base gas, characterized in that it comprises:
communication means for communicating between the said terminal and means containing at least one database which includes, for gas mixtures, data on the ternary diagrams of these mixtures, and the flammability regions in these diagrams as a function of the temperature and pressure conditions;
means for supplying the said terminal with data for the user of the said terminal, including at least one gas mixture used, and the temperature and pressure conditions of use, and optionally one or more types of defined mixers;
storage means, communicating with the means for supplying the said terminal with the user data, in order to store this user data, as well as data supplied by the database on the ternary diagram of the mixture selected;
display means, communicating with the storage means, in order to display at least the ternary diagram supplied by the database, and optionally the mixing time for a defined mixer.
The invention makes it possible, by consulting databases, to construct a set of information describing the behaviour of a gas mixture.
Thus, the arrangement of a plant intended for mixing gases may be quickly established, thereby shortening the design time for this plant.